Method and apparatus for monitoring electrical properties of polymerization reactor wall film

ABSTRACT

Disclosed is a method for using at least one static probe during polymerization in a fluid bed polymerization reactor system to monitor a coating on a surface of the reactor system and a distal portion of each static probe, wherein the coating is exposed to flowing fluid within the reactor system during the reaction. The surface may be a reactor bed wall (exposed to the reactor&#39;s fluid bed) and the coating is exposed to flowing, bubbling fluid within the fluid bed during the reaction. The method may include steps of: during the polymerization reaction, operating the static probe to generate a sequence of data values (“high speed data”) indicative of fluid flow variation (e.g., bubbling or turbulence), and determining from the high speed data at least one electrical property of the coating (e.g., of a portion of the coating on the distal portion of the static probe).

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 61/179,105, filed on May 18, 2009, the disclosure of which isincorporated by referenced in its entirety.

FIELD OF THE INVENTION

The invention pertains to methods for monitoring electrical propertiesof a fluid bed reactor wall, which may be coated with a film (e.g., apolymer film), during a polymerization (e.g., olefin polymerization)reaction in the reactor. Preferably, the methods are performed inon-line fashion during the reaction (e.g., using probes external to thereactor).

BACKGROUND

The expression “on-line” generation of data (or performance of anotheroperation) during a reaction herein denotes generation of the data (orperformance of the other operation) sufficiently rapidly so that thedata (or result of the operation) is available essentiallyinstantaneously or sometime thereafter for use during the reaction. Theexpression “generation of data in on-line fashion” during a reaction isused synonymously with the expression on-line generation of data duringa reaction. Generation of data from a laboratory test (on at least onesubstance employed or generated in the reaction) is not considered“on-line generation” of data during the reaction, if the laboratory testconsumes so much time that parameters of the reaction may changesignificantly during the time required to conduct the test. It iscontemplated that on-line generation of data may include the use of apreviously generated database that may have been generated in any of avariety of ways including time-consuming laboratory tests.

With reference to a product being produced by a continuous reaction, theexpression “instantaneous” value of a property of the product hereindenotes the value of the property of the most recently produced quantityof the product. Because of the back-mixed nature of a gas phasepolymerization reactor, the most recently produced polymer producttypically undergoes mixing with previously produced quantities ofproduct before a mixture of the recently and previously produced productexits the reactor. In contrast, with reference to a product beingproduced by a continuous reaction, the expression “average” (or “bedaverage”) value (at a time “T”) of a property herein denotes the valueof the property of the product that exits the reactor at time T.

The expression “polyethylene” denotes at least one polymer of ethyleneand optionally one or more C₃-C₁₀ α-olefins, while the expressionpolyolefin denotes at least one polymer (or copolymer) of one or moreC₂-C₁₀ α-olefins.

Throughout this disclosure, the abbreviation “MI” denotes melt index.Also throughout this disclosure, the term “density” denotes theintrinsic material density of a polymer product (in units of g/cc unlessotherwise stated), measured in accordance with ASTM-D-1505-98 unlessotherwise stated.

One method for producing polymers is gas phase polymerization. Aconventional gas phase fluidized bed reactor commonly employs afluidized dense-phase bed typically including a mixture of reaction gas,polymer (resin) particles, catalyst, and (optionally) other additives.Typically, any of several process control variables will cause thereaction product to have certain, preferably desired, characteristics.

Generally in a gas-phase fluidized bed process for producing polymersfrom monomers, a gaseous stream containing one or more monomers iscontinuously passed through a fluidized bed under reactive conditions inthe presence of an activated catalyst. This gaseous stream is optionallywithdrawn from the top of the fluidized bed and recycled back into thereactor. Simultaneously, polymer product is withdrawn from the reactorand new monomer is added to replace the polymerized monomer. Therecycled gas stream is heated in the reactor by the heat ofpolymerization. This heat is typically removed in another part of thecycle by a cooling system external to the reactor.

It is important to remove heat generated by the reaction in order tomaintain the temperature of the resin and gaseous stream inside thereactor at a temperature below the polymer melting point and/or catalystdeactivation temperature. Further, heat removal is important to controlthe reactor temperature to prevent excessive stickiness of polymerparticles that if left unchecked, may result in loss of fluidization oragglomeration of the sticky particles which may lead to formation ofchunks or sheets of fused polymer that cannot be removed as product.

Conventional fluid bed polymerization reactors often pretreated (e.g.,by “chromocene” treatment) to form a polymer film on the reactor wallsurfaces that will be exposed to polymer resin during normalpolymerization operation. Such a polymer film coating on the bed wall ofa pretreated reactor is intended to function as an insulating layer thatreduces static charging in the reactor system, thereby reducing thepotential for sheeting, during normal polymerization reactions. It isbelieved that static charging of polymer (e.g., polyethylene) resin inthe bed during polymerization is strongly influenced by the electricalinteraction between the polymer wall film and the reactor/cycle gas, andis thus strongly influenced by the electrical characteristics of thepolymer wall film. For example, a thick insulating wall film would limitcharge transfer from the polymer in the bed to ground.

Although the polymer wall film on a precoated reactor bed wall istypically thin (e.g., in a range from about 1 to about 20 mils, or 0.025to 0.50 millimeters, where one “mil” denotes 0.001 inches) and typicallydoes not have uniform thickness throughout the bed wall, it can beeffective in reducing static charging and is often durable. Often, atypically thin polymer film of this type has a service life of at leastfour years before retreatment is required, if (as is typical) the filmconsists of a high density, high molecular weight (very low melt index)polymer. Such a film having high density, high molecular weight, and lowmelt index, is typically highly resistant to abrasion by the softerpolymer typically present in the fluid bed during normal polymerizationoperation.

Conventional chromocene treatment methods can form effective andreliable polymer coatings on the bed walls of fluidized bedpolymerization reactors. Sometimes, however, such methods fail to formeffective and reliable polymer coatings and instead form insufficientlythick polymer on at least some bed wall portions. Without an effectivepolymer coating, a reactor that has undergone such failed treatment issensitive to static charging and sheeting, particularly duringpolymerization reactions using metallocene catalysts.

Also, the polymer coatings formed by conventional chromocene treatmentmethods on bed walls (of fluid bed polymerization reactors) candeteriorate or become contaminated over time. For example, they candeteriorate as a result of erosion and/or deposition of impuritiesthereon (e.g., decomposition products of aluminum alkyls). Suchdeterioration and/or contamination can have a major effect onoperability of the reactor. In practice, the reactor static baselinedoes not change suddenly due to the contamination or deterioration.Rather, the contamination or deterioration usually occurs over a periodof time and as this happens, static activity and sheeting problemsgradually develop and appear first during the production of certainresin products. These products, usually characterized as having highermolecular weights and higher densities, are referred to as the sensitivereactor grades. As the static baseline deteriorates further (e.g., asthe wall coating becomes more contaminated) static and sheeting problemsbegin to occur with more and more products. The sensitivity of sheetingrisk to different resin grades appears only with a contaminated ordeteriorated bed wall coating. It is desirable to operate the reactorwith the coating in good condition.

It is conventional to perform reactor system retreatment to remove a bad(deteriorated or contaminated) bed wall coating and replace it with anew polymer coating when necessary. Conventional retreatment methodsinvolve preparation of the bed wall (typically by removal of an existingbad polymer coating) and the in situ creation of a new polymer coatingon the wall. One such conventional retreatment method is theabove-mentioned chromocene treatment method; another is known ashydroblasting. Wall retreatment is expensive and requires reactorshutdown for retreatment. It would be desirable to have a reliablemethod for monitoring the state of an existing bed wall coating duringpolymerization operation of a reactor, e.g., to determine whenretreatment is or is not needed.

In the past, polymer coatings on the bed walls of fluidized bedpolymerization reactors were typically inspected on an opportunisticbasis (when the reactors were shut down) by persons who physicallyentered the reactor vessels with appropriate inspection instruments.Alternatively, the conventional metal coupon approach was used toinspect the coatings but this technique had to be performed in anoff-line fashion under conditions not necessarily representative ofactual operating conditions. There is a need for a method for monitoring(e.g., inspecting and/or characterizing) polymer coatings on bed wallsof fluid bed polymerization reactors (e.g., to assess whether thecoatings have deteriorated or become contaminated) during performance ofpolymerization reactions in the reactors (e.g., in on-line fashionduring each reaction using a probe external to the reactor).

Herein, the expression that a probe is “external” to a reactor (or is an“external” probe) denotes that the probe is configured and mounted so asneither to interfere significantly with nor significantly affect apolymerization reaction occurring in the reactor during operation of theprobe to monitor the reaction or reactor. For example, a probe having adistal portion (e.g., tip) that is flush with a bed wall of a reactor orextends slightly into the bed from the bed wall may be an “external”probe if the probe neither interferes significantly with nor otherwisesignificantly affects a polymerization reaction in the reactor while theprobe operates during the reaction to monitor voltage in the bed (or togenerate bed voltage data that is used to monitor a film that coats thebed wall and the probe's distal portion).

Herein, “bed static” denotes static charge (and/or the electricalpotential due to such charge) that is generated by frictional contactinvolving contents of a fluid bed polymerization reactor (e.g., polymerresin). For example, bed static can result from frictional contact ofpolymer resin in the bed with the reactor's bed wall (the wall in thefluidized bed section of the reactor). The bed wall can be coated oruncoated. It is conventional to monitor reactor bed static using probesexternal to the reactor. Static probes suitable for measuring bed staticare described in, for example, U.S. Pat. Nos. 6,008,662 and 6,905,654.

However, it had not been known how to use the output of one or morestatic probes (e.g., data indicative of voltage and/or current readings,generated using an external static probe) to monitor a property of acoating (e.g., polymer coating) on a bed wall of a fluid bedpolymerization reactor during performance of a polymerization reactionin the reactor (or to monitor a property of the bed wall itself duringperformance of the reaction in the reactor). Nor had it been known howto use the output of one or more static probes (e.g., external staticprobes) to assess whether such a coating (or the bed wall itself) hasdeteriorated or become contaminated.

In a class of embodiments, at least one static probe (e.g., an externalstatic probe) is used to monitor at least one property of a coating(typically a polymer coating) on a bed wall of a fluid bedpolymerization reactor (e.g., to assess whether the coating hasdeteriorated or become contaminated) during performance of apolymerization reaction in the reactor. In some embodiments, themonitoring is performed in on-line fashion during the reaction. In someembodiments the bed wall is not coated and at least one static probe isused to monitor at least one property of the wall itself (e.g., toassess whether the wall has deteriorated or become contaminated) duringperformance of the reaction.

A shortcoming of conventional static probes (for monitoring fluid bedpolymerization reactions) is that they measure only one of the followingtwo entirely different effects: (i) current flow by direct contact withthe bed (i.e., charge transfer from the bed to a probe surface); and(ii) inductive current flow (in which the electric field inside thereactor induces a charge on the probe surface without direct contactwith the probe). It would be desirable to measure both these effectssimultaneously at the same location in the bed.

SUMMARY

In a class of embodiments, the invention is a method for using at leastone static probe during performance of a polymerization reaction in afluid bed reactor system (sometimes referred to herein as a “reactor”for convenience), to monitor a coating on a surface of the reactorsystem and a distal portion of each static probe, where the coating isexposed to flowing fluid within the reactor system during performance ofthe method. Typically, the surface is a bed wall of the reactor (a wallexposed to the reactor's fluid bed) and the coating is exposed toflowing (e.g., bubbling) fluid within the fluid bed during the reaction.Typically, each static probe is an external probe mounted (e.g.,directly to the reactor) with its distal portion flush with the reactorbed wall or extending slightly into the fluid bed from the bed wall.Typically, the coating is a thin film of polymer (e.g., having thicknessless than 0.50 millimeters or in a range from about 0.025 to 0.50millimeters) that has been precoated on the bed wall and distal portionof each probe prior to performance of the reaction. In embodiments inwhich the coating to be monitored is on the reactor bed wall (and on adistal portion of each static probe), the method includes the steps of:

(a) during a first interval of time during performance of the reactionin the reactor system, operating the static probe to generate a sequenceof data values (sometimes referred to herein as “high speed data”)indicative of bubbling in the fluid bed. The high speed data typicallyinclude frequency components in a range (“bubbling frequency range”)from about 1 Hz to about 10 Hz, or from about 2 Hz to about 6 Hz, andthe duration of the first interval is typically at least one minute(e.g., several minutes); and

(b) determining from the high speed data at least one electricalproperty of the coating (e.g., at least one electrical property of aportion of the coating on the distal portion of the static probe).

The bubbling frequency range (for each static probe) is the range offrequencies of an electrical signal induced in the static probe bymovement of bubbles in the fluid bed relative to the static probe. Insome embodiments, the bubbling frequency range has been independentlydetermined (e.g., determined to be the bandwidth of bed DP readingsgenerated during the reaction or a polymerization reaction similarthereto, where each bed DP reading is a measured instantaneous pressuredifference between the bottom and top of the fluid bed), and each saidelectrical property of the coating is generated in step (b) fromfrequency components of the high speed data in a range that coincideswith or includes the independently determined bubbling frequency range.In some embodiments, the high speed data are generated by sampling theoutput of each static probe with a sampling frequency of at least 100Hz.

In some embodiments, at least one electrical property determined in step(b) is a breakdown voltage of the coating. In some embodiments, themethod also includes the step of:

(c) determining from at least one electrical property determined in step(b) at least one of a degree of deterioration of the coating and adegree of contamination of the coating. For example, step (c) caninclude the step of determining a degree of deterioration of the coatingfrom a determined breakdown voltage of the coating on the distal portionof the static probe.

In some embodiments, steps (a) and (b) (or all of steps (a), (b), and(c)) are performed in on-line fashion during the reaction. In someembodiments, the method also includes a step of determining from atleast one electrical property determined in step (b) whether to performretreatment of the surface, e.g., to remove the coating (e.g., becauseit has deteriorated or become contaminated to a sufficient degree) andreplace it with a new coating, or otherwise to reestablish a usefulcoating on the surface (e.g., by using a continuity aid to depositcoating material on the surface). In some embodiments, at least oneelectrical property determined in step (b) is or determines informationthat usefully characterizes at least one of the state of charge in thebed, the mechanism of charge generation, fluidization in the reactor,and the state of the coating.

In some embodiments, the first interval of time includes a set ofsubintervals, and step (b) includes the steps of:

determining standard deviation values, by determining for eachsubinterval in the set of subintervals, from the high speed datagenerated in said each subinterval of the first interval, the standarddeviation of the high speed data generated in the subinterval; and

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data and thestandard deviation values.

In other embodiments, the first interval of time includes a set ofsubintervals, the high speed data are indicative of average power drawnby the probe (due to current induced in the probe by charge in the fluidbed) during said each subinterval of the first interval, and step (b)includes the step of:

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data.

In some embodiments, the first interval of time includes a set ofsubintervals, and step (b) includes the steps of generating averageddata values from the high speed data by averaging, for each subintervalin the set of subintervals the high speed data generated in said eachsubinterval, and determining from the averaged data values and the highspeed data at least one said electrical property of the coating.

In another class of embodiments, the first interval of time includes aset of subintervals, and step (b) includes the steps of:

determining cross correlated (e.g., autocorrelated) values, bydetermining for said each subinterval of the first interval, a crosscorrelation of the high speed data generated in the subinterval with oneof said high speed data generated in the subinterval and a processedversion of said high speed data generated in the subinterval; and

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data and the crosscorrelated values.

The cross correlated values are indicative of movement of bubbles in thefluid bed past the probe. For example, when the cross correlated valuesare plotted (as voltages versus time), displacement voltages indicatedby the data values may be determined, where each such “displacementvoltage” consists of a peak (maximum) voltage followed with a lag time(e.g., in the range of 0.5 to 2 seconds) by a minimum voltage, or aminimum voltage followed (with a lag time in the same range) by amaximum voltage. In this example, a relative measure of bed static(voltage between the probe's coated distal portion and ground) isdetermined from the displacement voltages in a manner to be describedherein.

Static measurements performed will typically depend on both average bedstatic and fluidization (bubble size and velocity, and bednon-uniformities). Experience has shown that fluidization behavior isreproducible in the lower section of a typical polymerization reactorfluid bed, given the narrow range of gas velocities employedcommercially and proximity to the distributor plate (which controlsbubble formation), to typically determine accurately a relative measureof electrical potential in the lower section of such a fluid bed.Fluidization in the upper bed may be more variable and stronglydependent on coalescence of small bubbles to form large, fast bubbles.Thus, determination of a relative measure of electrical potential in theupper section of a fluid bed may be subject to greater uncertainty dueto fluidization effects than electrical potential in the upper sectionof a fluid bed.

In typical embodiments, the method includes the step of performingrepetitions of steps (a) and (b) sequentially, each performance of step(a) during a different time interval. For example, in some suchembodiments the method also includes the steps of:

(c) after step (a) but during a second interval of time duringperformance of the reaction in the reactor system, operating the staticprobe to generate an additional sequence of data values (referred toherein as “additional high speed data”) indicative of bubbling in thefluid bed;

(d) determining from the additional high speed data at least oneelectrical property of the coating; and

(e) in response to the electrical properties determined during steps (b)and (d), monitoring at least one of deterioration and contamination ofthe coating over time.

In some embodiments, the first interval of time includes a set ofsubintervals, the second interval of time includes a second set ofsubintervals, step (b) includes the steps of generating averaged datavalues from the high speed data by averaging, for each subinterval inthe set of subintervals, the high speed data generated in said eachsubinterval, and determining from the averaged data values and the highspeed data at least one said electrical property of the coating, andstep (d) includes the steps of generating additional averaged datavalues from the additional high speed data by averaging, for eachsubinterval in the second set of subintervals, the additional high speeddata generated in said each subinterval, and determining from theadditional averaged data values and the additional high speed data atleast one said electrical property of the coating.

In a class of embodiments, the invention is a bifunctional static probeconfigured for use in monitoring a polymerization reaction in a fluidbed reactor system, including:

an insulated probe having an electrically insulating distal portionconfigured to be exposed during said monitoring to flowing fluid withinthe reactor system (e.g., with the insulating distal portion having adistal surface flush with the bed wall or other reactor surface, orextending slightly into the fluid flow from the reactor surface) and aconductive proximal portion in contact with the distal portion; and

an electrically conducting bare probe, positioned coaxially with theinsulated probe and having an electrically conducting distal surfaceconfigured to be exposed during said monitoring to the flowing fluidwithin the reactor system (e.g., with the conducting distal surfaceflush with the bed wall or other reactor surface, or extending slightlyinto the fluid flow from the reactor surface).

Typically, the bare probe is at least substantially cylindrical, theinsulated probe is at least substantially annular, and the distalsurface of the bare probe is aligned with a distal surface of theinsulated probe's insulating distal portion. Preferably, the bare probehas a side surface, the insulated probe has an inner side surface facingthe bare probe's side surface, and the bifunctional static probeincludes an electrically insulating layer between the insulated probe'sinner side surface and the bare probe's side surface for insulating theinsulated probe from the bare probe. Typically, the insulated probe hasan electrically insulating outer side layer for insulating theconductive proximal portion from a conductive element of the reactorsystem (e.g., a bed wall) when the bifunctional static probe is mountedto such element.

The bifunctional probe is capable of measuring (preferablysimultaneously) direct current flow from the fluid bed of a reactor to asurface of the bare probe, and inductive current flow from the bed tothe insulated probe (without direct contact between the bed and aconductive element of the insulated probe). Measuring both these effectssimultaneously (or substantially simultaneously) at the same location inthe bed can provide information critical for characterizing the state ofcharge in the bed, the mechanism of charge generation, fluidization (viacapacitance measurements), and the state of wall coatings (e.g.,deposition, replenishment, deterioration, and contamination of a polymeror wax coating on a bare conductive distal surface of the probe, usingreadings from an insulated distal surface of the probe as reference).

Any of a variety of signal processing techniques may be employed toprocess the output of the inventive bifunctional static probe. Forexample, embodiments of the inventive method (described herein) canemploy the bifunctional probe to generate high speed data indicative ofbubbling in a fluid bed, and determine from the high speed data at leastone electrical property of a coating on a reactor wall and a distalportion of the probe (e.g., an electrical property of a portion of thecoating on the bare probe and the insulated probe of the bifunctionalprobe). In some cases, frequency analysis may be employed to extract(from the output of the bifunctional probe) the component of inductiondue to variations in local capacitance due to passage of bubbles. Inother cases, wavelet methods and/or short-term Fourier methods foranalysis of asynchronous signals may be used to extract a relativemeasure of bubbling-related charge density from the bifunctional probe'soutput. The absence of bubbling may indicate poor fluidization (similarto cold-banding) which may be a precursor to sheeting.

In some embodiments of the inventive monitoring method, the coating tobe monitored is not on a reactor bed wall. Instead the coating is onanother surface of a fluid bed reactor system (and on a distal portionof each static probe employed during the monitoring) exposed to flowingfluid during the reaction. For example, the coating may be on a surfacein the entrainment zone of the reaction system and the monitoring mayemploy at least one static probe positioned in the entrainment zone tomonitor carryover static. In this context, the expression “entrainmentzone” of a fluidized bed reactor system denotes any location in fluidbed polymerization reactor system outside the dense phase zone of thesystem (i.e., outside the fluid bed), and the expression “carryoverstatic” denote static charging that results from frictional contact byparticles (e.g., catalyst particles and resin particles) in theentrainment zone (e.g., against metal walls of the gas recycle line oragainst another component of the entrainment zone). In this class ofembodiments, the invention is a method for using at least one staticprobe during performance of a polymerization reaction in a fluid bedreactor system, to monitor a coating on an element of the entrainmentzone of the reactor system and a distal portion of each static probe.Typically, each static probe is an external probe mounted with itsdistal portion flush with the relevant entrainment zone element orextending slightly into the fluid flow from such element.

In a broader class of embodiments, the inventive method is a method forusing at least one static probe during performance of a polymerizationreaction in a fluid bed polymerization reactor system (sometimesreferred to herein as a “reactor”), to monitor a coating on a surface ofthe reactor system (e.g., the reactor's bed wall or a surface of thereactor's entrainment zone) and a distal portion of each static probe,where the coating is exposed to flowing fluid within the reactor systemduring performance of the method. In this class of embodiments, themethod includes the steps of:

(a) during performance of the reaction in the reactor system, operatingthe static probe to generate a sequence of data values (sometimesreferred to herein as “high speed data”) indicative of fluid flowvariation (e.g., bubbling or turbulence) during a first interval oftime; and

(b) determining from the high speed data at least one electricalproperty of the coating (e.g., of a portion of the coating on the distalportion of the static probe).

Any of the techniques described herein for determining an electricalproperty of a bed wall coating from high speed data may be employed todetermine an electrical property of a coating (e.g., on an entrainmentzone component) other than a bed wall coating, from the high speed datadetermined in this broader class of embodiments.

For example, in the broader class of embodiments, the high speed datamay include frequency components in a range from about 1 Hz to about 10Hz, or from about 2 Hz to about 6 Hz, and the duration of the firstinterval is much longer than the inverse of the lowest of thesefrequency components (e.g., the first interval may be several minutes ifthe lowest frequency component of interest in the high speed data is 1Hz). The frequency range of interest (for each static probe) is therange of frequencies of an electrical signal induced in the static probeby the fluid flow variation relative to the static probe during thereaction.

In some embodiments in the noted broader class, at least one electricalproperty determined in step (b) is a breakdown voltage of the coating.In some embodiments in the noted broader class, the method also includesthe step of: (c) determining from at least one electrical propertydetermined in step (b) at least one of a degree of deterioration of thecoating and a degree of contamination of the coating. For example, step(c) can include the step of determining a degree of deterioration of thecoating from a determined breakdown voltage of the coating on the distalportion of the static probe. In some embodiments in the noted broaderclass, steps (a) and (b) (or all of steps (a), (b), and (c)) areperformed in on-line fashion during the reaction.

Some embodiments of the inventive method employ the inventivebifunctional probe to generate high speed data. Other embodiments of theinventive method employ other static probes to generate high speed data(e.g., conventional static probes of the type described in U.S. Pat.Nos. 6,008,662 and 6,905,654).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified cross-sectional view of a reaction system,including fluidized bed reactor 4, with static probe assembly 2 mountedfor monitoring a coated bed wall of reactor 4, and static probe assembly2′ mounted for monitoring a coated cycle gas line 11 in accordance withseveral embodiments of the invention.

FIG. 2 is a simplified, enlarged cross-sectional view of probe 3 ofassembly 2 of FIG. 1 and a portion of bed wall 20 of reactor 4 of FIG.1, with a block diagram of other elements of assembly 2.

FIG. 3 is a graph of data generated by static probe assembly 2 of FIG. 1during monitoring of the bed wall of reactor 4 in accordance withseveral embodiments of the invention.

FIG. 4 is simplified, side cross-sectional view of a portion of anembodiment of the inventive bifunctional static probe mounted to the bedwall of a reactor.

FIG. 5 is a reduced, simplified version of FIG. 4 with a block diagramof additional elements of the bifunctional static probe.

DETAILED DESCRIPTION

Before the present compounds, components, compositions, devices,softwares, hardwares, equipments, configurations, schematics, systems,and/or methods are disclosed and described, it is to be understood thatunless otherwise indicated this invention is not limited to specificcompounds, components, compositions, devices, softwares, hardwares,equipments, configurations, schematics, systems, methods, or the like,as such may vary, unless otherwise specified. It is also to beunderstood that the terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

For the sake of brevity, the definitions and/or other informationprovided in the BACKGROUND and SUMMARY will not be repeated but arehereby incorporated into the DETAILED DESCRIPTION where applicable.

An example of a polymerization reactor system whose operation may bemonitored and optionally also controlled will be described withreference to FIG. 1. The FIG. 1 system includes fluidized bedpolymerization reactor 4. Reactor 4 has a top expanded (or “dome”)section which is composed of a cylindrical transition section and ahemispherical top head of the reactor, a distributor plate 10, acylindrical (straight) section between plate 10 and the top expandedsection, a gas inlet line 11, and a bottom section between gas inletline 11 and distributor plate 10. A fluidized bed 1 of granular polymerand catalyst particles is contained within the straight section. The bedis fluidized by a steady flow of recycle gas from inlet line 11 throughdistributor plate 10. Bubbles 1A move through bed 1 during typicalpolymerization operation. The flow rate of fluidizing gas is regulatedto provide the fluidized bed with relatively good mixing, as illustratedin the figure.

The reactor system also has a catalyst feeder (not shown) for controlledaddition of polymerization catalyst to the fluidized bed reaction zone.Within the reaction zone (i.e. the fluidized bed), the catalystparticles react with the ethylene, comonomer, and optionally hydrogenand other reaction gases to produce granular polymer particles. As newpolymer particles are produced, other polymer particles are continuallywithdrawn from the fluidized bed through a product discharge system 20.After passing through the product discharge system, the polymer granulesare degassed (or “purged”) with a flow of inert nitrogen to removesubstantially all of the dissolved hydrocarbon materials.

The reactor system of FIG. 1 also has a cooling control loop whichincludes a recycle gas line 13, compressor 6, and cycle gas cooler 12,coupled with reactor 4 as shown. During operation, the cooledcirculating gas from cooler 12 (which may contain condensed liquid)flows through inlet line 11 into reactor 4, then propagates upwardthrough the bed and out from reactor 4 via outlet 15. The cooler 12 ispreferably positioned downstream of compressor 6 (as shown in FIG. 1),but in some embodiments may be positioned upstream of compressor 6.

The expanded section is also known as the “velocity reduction zone” or“disengagement zone”, and is designed to minimize the quantities ofparticle entrainment from the fluidized bed. The diameter of eachhorizontal cross-section of the expanded section is greater than thediameter of the straight section. The increased diameter causes areduction in the speed of the fluidizing gas, which allows most of theentrained resin particles to settle back into the fluidized bed, therebyminimizing the quantities of solid particles that are entrained (or“carried over”) from the fluidized bed (at a given value of fluidizinggas velocity) through recycle gas line 13.

One or more static probe assemblies 2 (each including a probe 3) arepositioned for monitoring a coating 21 (shown in FIG. 2 but not FIG. 1)on the bed wall 20 of reactor 4. Bed wall 20 is the portion of reactor4's inner wall exposed to fluid bed 1 during a polymerization reaction.Coating 21 is typically a polymer coating preformed (e.g., by achromocene treatment) on bed wall 20 and on probe 3's distal portion(tip) prior to normal polymerization operation of the reactor system.Each probe 3 has a distal portion protruding slightly into fluid bed 1,or flush with bed wall 20 of reactor 4 but exposed to fluid bed 1. Onlyone static probe assembly 2 is shown for simplicity, but others may bemounted at other locations on bed wall 20.

Each of one or more static probe assemblies 2′ (each including a probe3′) is positioned for monitoring a coating on an entrainment zonesurface of the FIG. 1 system. One such assembly 2′ is shown in FIG. 1with the distal portion of its probe 3′ flush with the wall of inletline 11 and exposed to fluid flowing through line 11. Alternatively,probe 3′ has a distal portion protruding slightly into the interior ofline 11. A thin film 11A that coats the inner surface of line 11 alsocoats on a distal portion of probe 3′. Coating 11A on line 11 (and onthe distal portion of probe 3′) is exposed to fluid flow through line11. Only one static probe assembly 2′ is shown for simplicity, butothers may be mounted at other locations in the entrainment zone of theFIG. 1 system.

Other sensors, e.g., bed temperature sensors, are typically located inthe fluidized bed, and are used with a control system (not shown inFIG. 1) and an external cooling loop coupled to the heat exchanger 12 tocontrol the fluidized bed temperature Trx near the process set-point.Relatively warm reactor gas (which obtains a temperature substantiallyequal to that of the fluidized bed during its flow through reactor 4) iswithdrawn from outlet 15 and is pumped by compressor 6 to cooler 12,wherein the temperature of the gas (the cooling fluid) is reduced.Relatively cool fluid (which may contain condensed liquid) flows outfrom cooler 12 to the reactor inlet to cool the fluidized bed.Temperature sensors (not shown) near the inlet and outlet of cooler 12provide feedback to the control system regulate the amount by whichcooler 12 reduces the temperature of the fluid entering reactor.

The FIG. 1 system may also include a number of skin temperature sensors(typically implemented as thermocouple sensors having fast responsedesign), mounted in positions along the straight section of the reactorwall (and optionally also the conical portion of the expanded section)so as to protrude from the wall a short distance into the reactor (e.g.,3 to 12 mm) These sensors are configured and positioned to sense thetemperature T_(w) of the resin and/or reactor gas near the wall ofreactor 4 during operation.

Other sensors and optionally also other apparatus are typically alsoemployed to measure other reaction parameters during a polymerizationreaction. Such other reaction parameters preferably includeinstantaneous and bed-averaged resin product properties (e.g., meltindex and density of the polymer resin product being produced by theFIG. 1 system during a polymerization reaction). Bed-averaged resinproduct properties are conventionally measured by periodically samplingthe resin as it exits the reactor (e.g. once per hour), and performingthe appropriate tests in a quality control laboratory. Instantaneousproduct properties are conventionally determined by calculation methods(known in the art) based on reaction models specific to the particularcatalyst in use. The reaction models typically relate gas phaseconcentration ratios (e.g. the 1-hexene/ethylene molar ratio and thehydrogen/ethylene molar ratio) to the instantaneous density and meltindex of the polymer being produced.

Other measured reaction parameters preferably include reactor gascomposition, e.g., concentrations (and partial pressures) of allreactant gases and induced condensing agents (ICAs), as well as allinert gases (such as nitrogen, hydrocarbon inerts, etc.) that arepresent in relevant quantities. The reactor gas composition may bemeasured with a gas chromatographic system.

It is known how to regulate process variables to control varioussteady-state reactions performed by the FIG. 1 system (e.g., to controlgas phase composition, the concentration of induced condensing agents(ICAs) and, partial pressure of at least one reactant (e.g., ethylene),the type and properties of each catalyst introduced into reactor 4, andto use elements 6 and 12 in the manner described above to controltemperature). It is also known how to control a polymerization reactionduring a transition by regulating process control variables such thatthe product (granular polymer resin) has properties compliant with aninitial specification set at the start of the transition; the productproduced during the transition ceases to comply with the initialspecification set at a first time, and the product has propertiescompliant with a final specification set at the end of the transition.

FIG. 2 is a simplified, enlarged view of assembly 2 of FIG. 1. As shown,a thin polymer coating 21 (a thin film) coats bed wall 20 of reactor 4and the distal surface of probe 3. Generally cylindrical, elongatedprobe 3 is mounted with its coated distal surface flush with bed wall20's inner surface (the left surface in FIG. 2) so that probe 3′ coateddistal surface is exposed to the fluid bed during performance of areaction. Mounting flange 22 protrudes from the outer surface of wall 20around the proximal end of the channel (through wall 20) for receivingprobe 3. Housing 24 (partially shown) contains the major portion ofassembly 2, and fluid seal 23 between housing 24, flange 22, and probe 3prevents fluid leakage from the fluid bed.

Probe 3 comprises metal rod 9, and electrically insulating material 8around rod 9's cylindrical side surface. Insulating material 8 preventsdirect current flow between rod 9 and conductive (metal) wall 20, flange22, and housing 24.

Assembly 2 also includes electrometer 7 coupled between probe 3 (andthus probe 3's coated distal surface) and ground. Electrometer 7 (e.g.,a current meter or voltmeter) typically has very high resistance and isgrounded to wall 20 itself

Electrometer 7 is used to monitor readings from probe 3. Processor 5 iscoupled to electrometer 7 to sample the output of electrometer 7 andperform necessary processing on the sampled data to determine at leastone electrical property of coating 21. In typical implementations,electrometer 7 is an instrument or device capable of measuring flow ofcurrent induced in probe 3's tip to ground, and may be (for example) anammeter, picoammeter (a high sensitivity ammeter), or multi-meter.Current induced in probe 3's tip may also be determined indirectly bymeasuring the voltage generated by the current in passing through aresistor.

Preferably, processor 5 is programmed and otherwise configured to samplethe output of electrometer 7 and perform necessary processing on thesampled data to determine at least one electrical property of coating 21in on-line fashion. Electrical properties determined in on-line fashionare typically available for controlling the reaction without undesirabledelay. For example, an electrical parameter determined in on-linefashion may be used to trigger a change in relevant reaction parametersor even to trigger reactor shut down (e.g., to avoid an otherwiseimminent condition of excessive resin stickiness in the reactor).

Elements 3′, 5′, and 7′ of probe assembly 2′ of FIG. 1 correspond (andcan be identical) to elements 3, 5, and 7 of probe assembly 2. Assembly2′ can be implemented to be identical to assembly 2, but is mounted withthe coated distal surface of probe 3′ flush with the coated innersurface of line 11 (rather than with the coated inner surface of bedwall 20 as is probe 3 of assembly 2).

In accordance with an aspect of the invention, properties of a coatingon a bed wall (e.g., polymer film 21 on bed wall 20 of FIG. 1) of afluid bed polymerization reactor system, or a coating on an entrainmentzone surface of a fluid bed polymerization reactor system (e.g., coating11A on line 11 of the FIG. 1 system), can be determined using fast dataacquisition and analysis methods. The inventors have recognized that ahigh frequency static signal (e.g., static data generated by samplingthe output of a static probe with a sampling frequency of 100 Hz) isdominated by electrical induction when a gas bubble in the fluid bedpasses by the static probe. The gas bubble constitutes an absence ofelectrical charge passing by the probe and induces currents in the probevia Gauss's law. The characteristic frequencies of the static pulses arelower than those of the high speed data generated (using at least onestatic probe) and employed to monitor bed wall coating properties. Thecharacteristic frequencies of the static pulses induced by bubbletransits are in a range (sometimes referred to herein as a “bubblingfrequency range”) that is typically relatively low (e.g., from about 2Hz to about 6 Hz, or from 1 Hz to about 10 Hz during operation of afluid bed polyethylene polymerization reactor). High speed datagenerated for use in characterizing a bed wall coating should havefrequency components in the bubbling frequency range. For example, highspeed data generated by sampling the output of a static probe with asampling frequency at least twice the maximum frequency of the bubblingfrequency range (e.g., a sampling frequency of 100 Hz, where thebubbling frequency range is from 2 Hz to 6 Hz) has frequency componentsin the bubbling frequency range.

The high speed alternating current signal produced by a static probe dueto bubbling in the fluid bed is determined by factors including bubblesize and bubble velocity, as well as average electrical charge on thepolymer resin in the vicinity of the probe. In typical embodiments inwhich the polymerization reaction proceeds with operating conditions inthe narrow range typical in a commercial reactor, it is assumed thatvariations in average bubble size and average bubble velocity arenegligible. Having made this assumption, useful results are obtained.

Ohm's law is perhaps the simplest description of electrical propertiesof a material and is a starting point for understanding bed wall filmproperties. A simple conductor is said to obey Ohm's law if currentthrough the conductor increases linearly with voltage across theconductor. Semiconductors and insulators do not obey Ohm's law.

A useful method for determining electrical properties of a coating onthe bed wall of a polymerization reactor is to determine (from highspeed data generated using at least one static probe) the following twoquantities, at each of a sequence of times (e.g., in each of a sequenceof time windows) during a polymerization reaction in the reactor:

electrical potential in the fluid bed (since this quantity is typicallydetermined as the voltage between a coated distal portion of the probeand ground, the quantity will be referred to sometimes herein as “bedvoltage”); and

current through the coated distal portion of the probe from the bed toground (e.g., average current induced in the probe by charge in thefluid bed, in the relevant time window, drawn through the coated distalportion of the probe to ground).

The bed voltage values can be determined from measured high speed datain any of a variety of different ways described herein (e.g., fromstandard deviation values, covariance values, or cross correlated valuesdetermined from the high speed data, or from average power drawn by theprobe in the relevant frequency range as determined from the high speeddata using Fourier or wavelet methods or another method resulting in ameasure of noise).

The bed voltage values can be plotted versus the current values. FIG. 3is an example of such a plot, in which each plotted point represents bedvoltage and induced probe current during a different one of a sequenceof time windows during a polymerization reaction. More specifically, theposition of each plotted point along the vertical axis representsaverage current induced in the probe (e.g., probe 3 of FIGS. 1 and 2) bycharge in the fluid bed, in the relevant time window. The current isdrawn through the coated distal portion of the probe from the fluid bedto ground, measured (e.g., by electrometer 7 of FIG. 2), sampled andaveraged in appropriate time intervals (e.g., by processor 5 of FIG. 2)and is plotted (in FIG. 3) in arbitrary units. The position of eachplotted point along the horizontal axis of FIG. 3 represents average bedvoltage during the relevant time window, and is in arbitrary units.

FIG. 3 shows a curve fitted to the plotted points. As apparent from FIG.3, there is a bed voltage (referred to herein as a “breakdown voltage”of the coating on the probe's distal portion and the bed wall) abovewhich the curve is linear (with positive slope). The breakdown voltageis at about 0.33 units of bed voltage in FIG. 3. In the bed voltageregime above the breakdown voltage, the bed wall coating has theelectrical properties of a conductor (it obeys Ohm's law). In the bedvoltage regime below the breakdown voltage, the bed wall coating has theelectrical properties of an insulator (it does not obey Ohm's law).

Over weeks, months, and years of reactor operation, the breakdownvoltage and conductivity after breakdown of a bed wall coating willtypically evolve. For example, breakdown voltage has been observed toincrease after polymerization producing high MI polyethylene gradesusing a metallocene catalyst. We have also observed evolution of wallfilm layers in the “entrainment zones” of reactors (e.g., film layers onsurfaces of cycle gas lines) which change very slowly (e.g., over daysand weeks), probably due to low levels of scrubbing by passingparticles.

In a class of embodiments, the invention is a method for using at leastone static probe (e.g., probe 3 or probe 3′ of FIG. 1) duringperformance of a polymerization reaction in a fluid bed polymerizationreactor system (sometimes referred to herein as a “reactor” forconvenience), to monitor a coating on a surface of the reactor systemand a distal portion of each static probe, where the coating is exposedto flowing fluid within the reactor system during performance of themethod. Typically, the surface is a bed wall of the reactor (e.g., bedwall 20 of FIG. 2) exposed to the reactor's fluid bed, and the coating(e.g., coating 21 of FIG. 2) is exposed to flowing (e.g., bubbling)fluid within the fluid bed during the reaction. Typically, each staticprobe is an external probe mounted (e.g., directly to the reactor) withits distal portion flush with the reactor bed wall or extending slightlyinto the fluid bed from the bed wall. Typically, the coating is a thinfilm of polymer (e.g., having thickness in a range from about 0.025 to0.50 millimeters) that has been precoated on the bed wall and distalportion of each probe prior to performance of the reaction. Inembodiments in which the coating to be monitored (e.g., coating 21 ofFIG. 2) is on the reactor bed wall (e.g., bed wall 20 of FIG. 2) and ona distal portion of each static probe (e.g., the distal surface of probe3 of FIG. 2), the method includes the steps of:

(a) during a first interval of time during performance of the reactionin the reactor, operating the static probe to generate a sequence ofdata values (sometimes referred to herein as “high speed data”)indicative of bubbling in the fluid bed. The high speed data typicallyinclude frequency components in a range (“bubbling frequency range”)from about 1 Hz to about 10 Hz, or from about 2 Hz to about 6 Hz, andthe duration of the first interval is typically several minutes; and

(b) determining from the high speed data at least one electricalproperty of the coating (e.g., at least one electrical property of aportion of the coating on the distal portion of the static probe).

The bubbling frequency range (for each static probe) is the range offrequencies of an electrical signal induced in the static probe bymovement of bubbles in the fluid bed relative to the static probe. Insome embodiments, the bubbling frequency range has been independentlydetermined (e.g., determined to be the bandwidth of bed DP readingsgenerated during the reaction or a polymerization reaction similarthereto, where each bed DP reading is a measured instantaneous pressuredifference between the bottom and top of the fluid bed), and each saidelectrical property of the coating is generated in step (b) fromfrequency components of the high speed data in a range that coincideswith or includes the independently determined bubbling frequency range.In some embodiments, the high speed data are generated by sampling theoutput of each static probe with a sampling frequency of at least 100Hz.

In some embodiments, at least one electrical property determined in step(b) is a breakdown voltage of the coating. In some embodiments, themethod also includes the step of:

(c) determining from at least one electrical property determined in step(b) at least one of a degree of deterioration of the coating and adegree of contamination of the coating. For example, step (c) caninclude the step of determining a degree of deterioration of the coatingfrom a determined breakdown voltage of the coating on the distal portionof the static probe.

In some embodiments, steps (a) and (b) (or all of steps (a), (b), and(c)) are performed in on-line fashion during the reaction.

In some embodiments, the first interval of time includes a set ofsubintervals, and step (b) includes the steps of:

determining standard deviation values, by determining for eachsubinterval in the set of subintervals, from the high speed datagenerated in said each subinterval of the first interval, the standarddeviation of the high speed data generated in the subinterval; and

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data and thestandard deviation values. For example, processor 5 of FIG. 2 isprogrammed to determine such standard deviation values from the sampledoutput of electrometer 7 and to determine the electrical potential inthe fluid bed from such standard deviation values and sampled outputdata.

In other embodiments, the first interval of time includes a set ofsubintervals, the high speed data are indicative of average power drawnby the probe (due to current induced in the probe by charge in the fluidbed) during said each subinterval of the first interval, and step (b)includes the step of:

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data. For example,processor 5 of FIG. 2 is programmed to determine such average powervalues from the sampled output of electrometer 7 and to determine theelectrical potential in the fluid bed from such values and sampledoutput data. In some embodiments, Fourier or wavelet methods are used,or another method resulting in a measure of noise is used, to determinethe average power drawn by the probe in the relevant frequency range.

In some embodiments, the first interval of time includes a set ofsubintervals, and step (b) includes the steps of generating averageddata values from the high speed data by averaging, for each subintervalin the set of subintervals the high speed data generated in said eachsubinterval, and determining from the averaged data values and the highspeed data at least one said electrical property of the coating.

In another class of embodiments, the first interval of time includes aset of subintervals, and step (b) includes the steps of:

determining cross correlated (e.g., autocorrelated) values, bydetermining for said each subinterval of the first interval, a crosscorrelation of the high speed data generated in the subinterval with oneof said high speed data generated in the subinterval and a processedversion of said high speed data generated in the subinterval; and

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data and the crosscorrelated values. For example, processor 5 of FIG. 2 is programmed todetermine such cross correlated values from the sampled output ofelectrometer 7 and to determine the electrical potential in the fluidbed from such cross correlated values and sampled output data.

In some embodiments in the latter class, cross correlation calculationsare performed using the function “xcorr” in the commercially availableMatlab software (available from The MathWorks). Alternatively, the crosscorrelation calculations are performed on a computer or other processingsystem (e.g., processor 5 of FIG. 2) programmed in another appropriatemanner. To calculate the cross correlation of vectors x and y (of equalsize) using the Matlab software, the command “output=xcorr(x,y)” isexecuted in the Matlab environment. Autocorrelation of vector x withitself is performed as a special case, using the command“output=xcorr(x)”.

For example, high speed static data are collected for five minutesduring performance of a polymerization reaction by operating processor 5(of FIG. 2) to sample the output of electrometer 7 (of the static probeassembly of FIG. 2) with a sampling frequency of 100 Hz, thus producinga vector of 30,000 data values. Cross correlation is performed asfollows to determine voltage between the probe's coated distal portionand ground (which is taken as a measure of electrical potential in thefluid bed):

(i) zero offsets and baseline drift are removed from the data values(e.g., using the “detrend” function of the Matlab software) to determinea detrended vector;

(ii) the absolute values of the data values of the detrended vector aredetermined, thus determining an absolute valued vector;

(iii) the detrended vector and the absolute valued vector arecross-correlated, thereby determining a cross correlation vector.

The cross correlation vector is indicative of movement of bubbles in thefluid bed past the probe. For example, when the data values of the crosscorrelation vector are plotted (as voltages versus time), and“displacement voltages” indicated by the data values are determined,where each such “displacement voltage” consists of a peak (maximum)voltage followed with a lag time (in the range of 0.5 to 2 seconds) by aminimum voltage, or a minimum voltage followed (with a lag time in thesame range) by a maximum voltage. This lag time range is for a typicalpolymerization reaction with typical superficial gas velocity. Ingeneral, the appropriate lag time range depends on the superficial gasvelocity in the reactor.

Covariance is a well known parameter related to cross-correlation.Covariance values rather than cross correlated values are determined insome embodiments of the invention. Thus, in some embodiments, the firstinterval of time includes a set of subintervals, and step (b) includesthe steps of:

determining covariance values, by determining for said each subintervalof the first interval, covariance of the high speed data generated inthe subinterval with one of said high speed data generated in thesubinterval and a processed version of said high speed data generated inthe subinterval; and

determining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data and thecovariance values.

A relative measure of bed static (voltage between the probe's coateddistal portion and ground) is determined from the displacement voltagesas follows. From each displacement voltage, a relative measure of thevoltage between the probe's coated distal portion and ground at the timeof occurrence of the displacement voltage (e.g., the time of occurrenceof the leading voltage extremum) is the magnitude of the leading voltageextremum (max or min) of the displacement voltage minus the magnitude ofthe lagging voltage extremum (max or min) This method is especiallyuseful because the sign of the average resin charge is retained.

Static measurements performed (e.g., those described in the foregoingexample) will typically depend on both average bed static andfluidization (bubble size and velocity, and bed non-uniformities).Experience has shown that fluidization behavior is reproducible in thelower section of a typical polymerization reactor bed, given the narrowrange of gas velocities employed commercially and proximity to thedistributor plate (which controls bubble formation), to typicallydetermine accurately a relative measure of electrical potential in thelower section of such a fluid bed. Fluidization in the upper bed may bemore variable and strongly dependent on coalescence of small bubbles toform large, fast bubbles. Thus, determination of a relative measure ofelectrical potential in the upper section of a fluid bed may be subjectto greater uncertainty due to fluidization effects than electricalpotential in the upper section of a fluid bed.

In typical embodiments, the method includes the step of performingrepetitions of steps (a) and (b) sequentially, each performance of step(a) during a different time interval. For example, in some suchembodiments the method also includes the steps of:

(c) after step (a) but during a second interval of time duringperformance of the reaction in the reactor, operating the static probeto generate an additional sequence of data values (referred to herein as“additional high speed data”) indicative of bubbling in the fluid bed;

(d) determining from the additional high speed data at least oneelectrical property of the coating; and

(e) in response to the electrical properties determined during steps (b)and (d), monitoring at least one of deterioration and contamination ofthe coating over time.

In some embodiments, the first interval of time includes a set ofsubintervals, the second interval of time includes a second set ofsubintervals, step (b) includes the steps of generating averaged datavalues from the high speed data by averaging, for each subinterval inthe set of subintervals, the high speed data generated in said eachsubinterval, and determining from the averaged data values and the highspeed data at least one said electrical property of the coating, andstep (d) includes the steps of generating additional averaged datavalues from the additional high speed data by averaging, for eachsubinterval in the second set of subintervals, the additional high speeddata generated in said each subinterval, and determining from theadditional averaged data values and the additional high speed data atleast one said electrical property of the coating.

Another aspect of the invention is a bifunctional static probeconfigured for use in monitoring a polymerization reaction in a fluidbed reactor. A typical embodiment of such a probe, bifunctional staticprobe 40, will be described with reference to FIGS. 4 and 5.

As shown in FIG. 4, probe 40 includes:

an insulated probe 46 having an electrically insulating distal portion41 configured to be exposed during use to flowing fluid within thereactor (with insulating distal portion 41's distal surface at leastsubstantially flush with the reactor's bed wall 30) and a conductiveproximal portion 45 in contact with distal portion 41; and

an electrically conducting bare probe 44, positioned coaxially with theinsulated probe and having an electrically conducting distal surface 42configured to be exposed during use to the flowing fluid within thereactor (e.g., with the conducting distal surface at least substantiallyflush with the reactor's bed wall 30).

Alternatively, the distal portions of the insulated and conductingprobes can extend slightly into the fluid flow from a reactor surface(typically, the bifunctional probe is mounted to a reactor element at ornear to this surface).

Bare probe 44 (of FIGS. 4 and 5) is substantially cylindrical, insulatedprobe 46 is substantially annular, and distal surface 42 of bare probe44 is aligned with the annular distal surface of probe 46's insulatingdistal portion 41. Bare probe 44 has a generally cylindrical outer sidesurface. Insulated probe 46 has a generally cylindrical, inner sidesurface coated with an electrically insulating layer 47. When probe 40is assembled, layer 47 faces bare probe 44 and insulates probe 44 frominsulated probe 46. Insulated probe 46's outer side surface is coatedwith an electrically insulating layer 48. When probe 40 is assembled andmounted to the reactor bed wall 30, layer 48 faces wall 30 and insulatesprobe 40 therefrom.

As shown in FIG. 5, bifunctional static probe 40 also includes readoutcircuitry 50 coupled to the conductive proximal portion 45 of insulatedprobe 46 and to bare probe 44. Circuitry 50 is configured to assert abare probe output (indicative of at least one of current through bareprobe 44 and voltage across bare probe 44) and an insulated probe output(indicative of at least one of current through insulated probe 46 andvoltage across probe 46), e.g., to data logging and control systems.Circuitry 50 is preferably configured to assert the bare probe outputsimultaneously with the insulated probe output. Alternatively, circuitry50 is configured to assert the bare probe output and the insulated probeoutput sequentially (e.g., in time division multiplexed fashion). In theFIG. 5 embodiment, readout circuitry 50 is an ammeter connected betweenground (bed wall 30) and probes 44 and 46. More generally, the readoutcircuitry of the inventive bifunctional probe may be or include anelectrometer (e.g., a current meter or voltmeter) coupled to theconductive proximal portion of the insulated probe and to the bareprobe. Typically, the readout circuitry is coupled during use betweenthe conductive proximal portion of the insulated probe and ground, andbetween the bare probe and ground. The readout circuitry should presenta very high resistance to the bifunctional probe to prevent drainage ofsufficient charge to impact the sensing element and the very processeswhich the probe is designed to measure. The readout circuitry's output(preferably a voltage across a very large resistor) is preferablyasserted to a transmitter via a shielded coax cable. Transmitted signalsfrom both the insulated and bare probes of the inventive bifunctionalprobe can be asserted to control system computers for logging, analysisand control action (e.g., to manipulate flow of continuity aid).

Bifunctional probe 40 is capable of measuring (preferablysimultaneously) direct current flow from the fluid bed of a reactor todistal surface 42 of bare probe 44, and inductive current flow from thebed to insulated probe 46 (without direct contact between the bed and aconductive element of probe 46). Measuring both these effectssimultaneously (or substantially simultaneously) at the same location inthe bed can provide information critical for characterizing the state ofcharge in the bed, the mechanism of charge generation, fluidization (viacapacitance measurements), and the state of wall coatings (e.g.,deposition, replenishment, deterioration, and contamination of a polymeror wax coating on a bare conductive distal surface of the probe, usingreadings from an insulated distal surface of the probe as reference).

Since both the bare probe (e.g., probe 44 of FIG. 5) and insulated probe(e.g., probe 46 of FIG. 5) should measure the same locale in the reactorsystem (e.g., in the reactor's fluid bed), they preferably are mountedcoaxially with respect to each other (as in the embodiment of FIGS. 4and 5). When the inventive bifunctional probe is used to monitor thefluid bed (or a coating on the bed wall and a distal surface of theinsulated probe and bare probe thereof) the distal surfaces of thebifunctional probe's insulated probe and bare probe should be smallerthan the typical bubble size in the fluid bed.

The composition of electrically insulating distal portion 41 (ofinsulated probe 46) may influence the contact charging measurementsdetermined using bare probe 44. In some cases it will be desirable toeliminate or minimize this influence; in other cases the influence maybe desirable. Thus, it may be desirable in some applications for distalportion 41 to be composed of material that is triboelectrically matchedto material expected to come into contact with it during use (e.g.,polymer being produced in the fluid bed) to eliminate or minimizetriboelectric charging of materials contacting distal portion 41 duringoperation of probe 44 and/or probe 46. Alternatively, it may bedesirable in other applications to form distal portion 41 of materialthat is triboelectrically dissimilar to material (e.g., polymer beingproduced in the fluid bed) expected to come into contact with portion 41during operation, to allow a useful amount of triboelectric charging ofmaterials contacting distal portion 41 during operation of probe 44and/or probe 46.

For example, when probes 44 and 46 are expected to operate duringproduction of polyethylene (“PE”) within a fluid bed reactor (e.g., thereactor whose wall 30 is shown in FIG. 4), it may be desirable to formdistal portion 41 of insulating material that is triboelectricallydissimilar to the PE particles that will come into contact with itduring operation. This would allow distal portion 41 to contact-chargesome of the PE particles that contact it during operation, so that aportion of the resulting charge would dissipate through bare probe 44,possibly allowing the output of probe 44 to provide useful informationnot attainable if distal portion 41 were triboelectrically matched tothe PE particles.

To normalize signal strength, the cross-sectional areas of theconductive elements of both the bare probe (e.g., probe 44 of FIG. 5)and insulated probe (e.g., probe 46 of FIG. 5) of the inventivebifunctional probe may be identical. The insulated probe is preferablyruggedized to ensure that its insulating distal portion will not beremoved or abraded by years of contact reactor system fluid (e.g., thecontents of a fluidized bed). The inventive bifunctional probe willlikely need to be removed from service during wall cleaning operations(such as sandblasting) to prevent damage to the insulating distalportion of its insulating probe.

Typical embodiments of the bifunctional probe are useful by plantpersonnel to compare readings of a type generated by a traditional(non-insulated) static probe with readings generated by an insulatedstatic probe, e.g., in order to verify the condition of a thin coatingon a reactor wall (and on a distal portion of each of the non-insulatedand insulated probes). For example, probe assembly 2 (and/or probeassembly 2′) of FIG. 1 can be implemented as a bifunctional probe (e.g.,of the type shown in FIG. 5) and employed to perform any of theinventive monitoring methods described herein.

Typical embodiments of the bifunctional probe can be used to monitorplant events which impact a bed wall coating. Different polymer gradesand different catalysts may remove or deposit polymer on reactorsurfaces (including surfaces of static probes that are exposed to thefluid bed), leading to an evolution of wall condition. Accordingly,static generation and dissipation will evolve. It is expected that amore complete and detailed understanding of wall condition (e.g., viaon-line monitoring) may lead to better methods for wall management, andmay delay or eliminate the need for chromocene treatment.

More fundamentally, at least some embodiments of the inventivebifunctional probe can be used by technologists to decouple inductiveand charge-transfer measurements, thereby providing a clearerunderstanding of static charge and the mechanisms of static chargegeneration and dissipation, free of the static noise caused by localvariations in bed capacitance due to fluidization and bubbling. It isexpected that this understanding will bring clearer focus on staticcontrol technologies such as continuity aids and antistats. A secondbenefit is the clearer understanding of fluidization and bubbling in thefluid bed.

Any of a variety of signal processing techniques may be employed toprocess the output of the inventive bifunctional static probe. Forexample, embodiments of the inventive method (described herein) canemploy the bifunctional probe to generate high speed data indicative ofbubbling in a fluid bed, and determine from the high speed data at leastone electrical property of a coating on a reactor wall and a distalportion of the probe (e.g., an electrical property of a portion of thecoating on the bare probe and the insulated probe of the bifunctionalprobe). In some cases, frequency analysis may be employed to extract(from the output of the bifunctional probe) the component of inductiondue to variations in local capacitance due to passage of bubbles. Inother cases, wavelet methods and/or short-term Fourier methods foranalysis of asynchronous signals may be used to extract a relativemeasure of bubbling-related charge density from the bifunctional probe'soutput. The absence of bubbling may indicate poor fluidization (similarto cold-banding) which may be a precursor to sheeting.

As noted, in some embodiments of the inventive method the coating to bemonitored is not on a reactor bed wall. Instead the coating is onanother surface of a fluid bed reactor system (and on a distal portionof each static probe employed during the monitoring) exposed to flowingfluid during the reaction. For example, the coating may be on a surfacein the entrainment zone of the reaction system (e.g., the coating iscoating 11A on the inner surface of line 11 of the FIG. 1 system) andthe monitoring may employ at least one static probe positioned in theentrainment zone to monitor carryover static (e.g., probe 3′ of probeassembly 2′ of FIG. 1). In this context, the expression “entrainmentzone” of a fluidized bed reactor system denotes any location in fluidbed polymerization reactor system outside the dense phase zone of thesystem (i.e., outside the fluid bed), and the expression “carryoverstatic” denote static charging that results from frictional contact byparticles (e.g., catalyst particles and resin particles) in theentrainment zone (e.g., against metal walls of the gas recycle line oragainst another component of the entrainment zone). In this class ofembodiments, the invention is a method for using at least one staticprobe during performance of a polymerization reaction in a fluid bedpolymerization reactor, to monitor a coating on an element of theentrainment zone of the reactor and a distal portion of each staticprobe. Typically, each static probe is an external probe mounted withits distal portion flush with the relevant entrainment zone element orextending slightly into the fluid flow from such element.

In a broader class of embodiments, the inventive method is a method forusing at least one static probe during performance of a polymerizationreaction in a fluid bed polymerization reactor system (sometimesreferred to herein as a “reactor”), to monitor a coating on a surface ofthe reactor system (e.g., the reactor's bed wall or a surface of thereactor's entrainment zone) and a distal portion of each static probe,where the coating is exposed to flowing fluid within the reactor systemduring performance of the method. In this class of embodiments, themethod includes the steps of:

(a) during performance of the reaction in the reactor, operating thestatic probe to generate a sequence of data values (sometimes referredto herein as “high speed data”) indicative of fluid flow variation(e.g., bubbling or turbulence) during a first interval of time; and

(b) determining from the high speed data at least one electricalproperty of the coating (e.g., of a portion of the coating on the distalportion of the static probe).

Any of the techniques described herein for determining an electricalproperty of a bed wall coating from high speed data may be employed todetermine an electrical property of a coating (e.g., on an entrainmentzone component) other than a bed wall coating, from the high speed datadetermined in this broader class of embodiments.

For example, in the broader class of embodiments, the high speed datamay include frequency components in a range from about 1 Hz to about 10Hz, or from about 2 Hz to about 6 Hz, and the duration of the firstinterval is much longer than the inverse of the lowest of thesefrequency components. For example, the first interval may be at leastone minute (e.g., several minutes) if the lowest frequency component ofinterest in the high speed data is 1 Hz. The frequency range of interest(for each static probe) is the range of frequencies of an electricalsignal induced in the static probe by the fluid flow variation relativeto the static probe during the reaction.

In some embodiments in the noted broader class, at least one electricalproperty determined in step (b) is a breakdown voltage of the coating.In some embodiments in the broader class, the method also includes thestep of:

(c) determining from at least one electrical property determined in step(b) at least one of a degree of deterioration of the coating and adegree of contamination of the coating. For example, step (c) caninclude the step of determining a degree of deterioration of the coatingfrom a determined breakdown voltage of the coating on the distal portionof the static probe. In some embodiments in the noted broader class,steps (a) and (b) (or all of steps (a), (b), and (c)) are performed inon-line fashion during the reaction.

Some embodiments of the inventive method employ the inventivebifunctional probe to generate high speed data. Other embodiments of theinventive method employ other static probes to generate high speed data(e.g., conventional static probes of the type described in U.S. Pat.Nos. 6,008,662 and 6,905,654).

We next describe examples of commercial-scale reactions (e.g.,commercial-scale, gas-phase fluidized-bed polymerization reactions) thatcan be monitored and optionally also controlled. Some such reactions canoccur in a reactor having the geometry of reactor 4 of FIG. 1.Performance of any of a variety of different reactors can be monitoredin accordance with different embodiments of the invention.

In some embodiments, a continuous gas phase fluidized bed reactor ismonitored and optionally also controlled while it operates to performpolymerization as follows; the fluidized bed is made up of polymergranules. Gaseous feed streams of the primary monomer and hydrogentogether with liquid or gaseous comonomer are mixed together in a mixingtee arrangement and introduced below the reactor bed into the recyclegas line. For example, the primary monomer is ethylene and the comonomeris 1-hexene. The individual flow rates of ethylene, hydrogen andcomonomer are controlled to maintain fixed gas composition targets. Theethylene concentration is controlled to maintain a constant ethylenepartial pressure. The hydrogen is controlled to maintain a constanthydrogen to ethylene mole ratio. The hexene is controlled to maintain aconstant hexene to ethylene mole ratio (or alternatively, the flow ratesof comonomer and ethylene are held at a fixed ratio). The concentrationof all gases is measured by an on-line gas chromatograph to ensurerelatively constant composition in the recycle gas stream. A solid orliquid catalyst is injected directly into the fluidized bed usingpurified nitrogen as a carrier. The feed rate of catalyst is adjusted tomaintain a constant production rate. The reacting bed of growing polymerparticles is maintained in a fluidized state by a continuous flow ofmake up feed and recycle gas through the reaction zone (i.e. thefluidized bed).

In some implementations, a superficial gas velocity of 2.0 to 2.8 ft/secis used to achieve this, and the reactor is operated at a total pressureof 300 psig. To maintain a constant reactor temperature, the temperatureof the recycle gas is continuously adjusted up or down to accommodateany changes in the rate of heat generation due to the polymerization.The fluidized bed is maintained at a constant height by withdrawing aportion of the bed at a rate equal to the rate of formation ofparticulate product. The product is removed semi-continuously via aseries of valves into a fixed volume chamber, which is simultaneouslyvented back to the reactor. This allows for efficient removal of theproduct, while at the same time recycling a large portion of theunreacted gases back to the reactor. This product is purged to removeentrained and dissolved hydrocarbons and treated with a small steam ofhumidified nitrogen to deactivate any trace quantities of residualcatalyst.

In other embodiments, a reactor is monitored and optionally alsocontrolled while it operates to perform polymerization using any of avariety of different processes (e.g., slurry, or gas phase processes).For example, the reactor can be a fluidized bed reactor operating toproduce polyolefin polymers by a gas phase polymerization process. Thistype of reactor and means for operating such a reactor are well known.In operation of such reactors to perform gas phase polymerizationprocesses, the polymerization medium can be mechanically agitated orfluidized by the continuous flow of the gaseous monomer and diluent.

In some embodiments, a polymerization reaction that is a continuous gasphase process (e.g., a fluid bed process) is monitored and optionallyalso controlled. A fluidized bed reactor for performing such a processtypically comprises a reaction zone and a velocity reduction zone (alsoknown as an expanded section). The reaction zone comprises a bed ofgrowing polymer particles, formed polymer particles and a minor amountof catalyst particles fluidized by a continuous flow of reactor gasthrough the reaction zone. Optionally, some of the recirculated gasesmay be cooled and compressed to form liquids that increase the heatremoval capacity of the circulating gas stream when readmitted to thereaction zone. This method of operation is referred to as “condensedmode.” A suitable rate of gas flow may be readily determined by simpleexperiment. Make up of gaseous monomer, comonomer and hydrogen to thecirculating gas stream is at a rate equal to the rate at whichparticulate polymer product and monomer associated therewith iswithdrawn from the reactor, so as to maintain an essentially steadystate gaseous composition within the reaction zone. The gas leaving thereaction zone is passed to the velocity reduction zone where entrainedparticles are removed. Finer entrained particles and dust may be removedin a cyclone and/or fines filter. The gas is compressed in a compressorand passed through a heat exchanger wherein the heat of polymerizationis removed, and then returned to the reaction zone.

The reactor temperature (Trx) of the fluid bed process is normallyoperated at the highest temperature that is feasible, given thestickiness or sintering characteristics of the polymer in the fluid bedto maximize heat removal capabilities.

In other embodiments, a reactor whose operation is monitored andoptionally also controlled effects polymerization by a slurrypolymerization process. Non-limiting examples of slurry processesinclude continuous loop or stirred tank processes. A slurrypolymerization process generally uses pressures in the range of from 1to 50 atmospheres, and temperatures in the range of 0° C. to 120° C.,and more particularly from 30° C. to 100° C. In a slurry polymerizationprocess, a slurry of solid, particulate polymer is formed in a liquidpolymerization diluent medium to which monomer, comonomers, catalyst,and often hydrogen are added. The slurry including diluent isintermittently or continuously removed from the reactor where thevolatile components are separated from the polymer and recycled,optionally after a distillation, to the reactor. The liquid diluentemployed in the polymerization medium is typically an alkane having from3 to 7 carbon atoms, a branched alkane in one embodiment. The mediumemployed should be liquid under the conditions of polymerization andchemically non-reactive with the catalyst and monomers employed in thereactor system. In some embodiments, a hexane, isopentane or isobutanediluent is employed.

In other embodiments, a reaction monitored and optionally alsocontrolled is or includes particle from polymerization, or a slurryprocess in which the temperature is kept below the temperature at whicha substantial portion of the polymer goes into solution. In someembodiments, a particle form polymerization reaction monitored andoptionally also controlled is a slurry loop reactor, in which acirculation pump is employed to circulate the slurry through heatexchanger tubes to remove the heat of polymerization. In the slurry loopembodiment, the temperature and pressure of the slurry polymerizationprocess are preferably operated above the thermodynamic critical pointof the diluent to avoid the possibility of cavitation in the slurrycirculation pump. In other embodiments, a reaction monitored andoptionally also controlled is carried out in a plurality of slurry loopreactors or stirred tank reactors in series, parallel, or combinationsthereof.

A reaction monitored and optionally also controlled in accordance withsome embodiments of the invention can produce homopolymers of olefins(e.g., homopolymers of ethylene), and/or copolymers, terpolymers, andthe like, of olefins, particularly ethylene, and at least one otherolefin. The olefins, for example, may contain from 2 to 16 carbon atomsin one embodiment; or ethylene and a comonomer comprising from 3 to 12carbon atoms in another embodiment; or ethylene and a comonomercomprising from 4 to 10 carbon atoms in yet another embodiment; orethylene and a comonomer comprising from 4 to 8 carbon atoms in yetanother embodiment. A reaction monitored and optionally also controlledproduce polyethylene. Such polyethylene can be homopolymers of ethyleneand interpolymers of ethylene and at least one α-olefin wherein theethylene content is at least about 50% by weight of the total monomersinvolved. Exemplary olefins that may be utilized in embodiments of theinvention are ethylene, propylene, 1-butene, 1-pentene, 1-hexene,1-heptene, 1-octene, 4-methylpent-1-ene, 1-decene, 1-dodecene,1-hexadecene and the like. Also utilizable herein are polyenes such as1,3-hexadiene, 1,4-hexadiene, cyclopentadiene, dicyclopentadiene,4-vinylcyclohex-1-ene, 1,5-cyclooctadiene, 5-vinylidene-2-norbornene and5-vinyl-2-norbornene, and olefins formed in situ in the polymerizationmedium. When olefins are formed in situ in the polymerization medium,the formation of polyolefins containing long chain branching may occur.

In the production of polyethylene or polypropylene, one or morecomonomers may be present in the polymerization reactor. When present,the comonomer may be present at any level with the ethylene or propylenemonomer that will achieve the desired weight percent incorporation ofthe comonomer into the finished resin. In one embodiment of polyethyleneproduction, the comonomer is present with ethylene in a mole ratio rangein the gas phase of from 0.0001 (comonomer:ethylene) to 50, and from0.0001 to 5 in another embodiment, and from 0.0005 to 1.0 in yet anotherembodiment, and from 0.001 to 0.5 in yet another embodiment. Expressedin absolute terms, in making polyethylene, the amount of ethylenepresent in the polymerization reactor may range to up to 1000atmospheres pressure in one embodiment, and up to 500 atmospherespressure in another embodiment, and up to 100 atmospheres pressure inyet another embodiment, and up to 50 atmospheres in yet anotherembodiment, and up to 10 atmospheres in yet another embodiment.

Hydrogen gas is often used in olefin polymerization to control the finalproperties of the polyolefin. For some types of catalyst systems, it isknown that increasing concentrations (or partial pressures) of hydrogenreduce the molecular weight and increase the melt index (MI) of thepolyolefin generated. The MI can thus be influenced by the hydrogenconcentration. The amount of hydrogen in the polymerization can beexpressed as a mole ratio relative to the dominant polymerizable monomerthat is present in the reactor; for example, ethylene or propylene. Theamount of hydrogen used in some polymerization processes is an amountnecessary to achieve the desired MI (or molecular weight) of the finalpolyolefin resin. In one embodiment, the mole ratio in the gas phase ofhydrogen to total monomer (H₂:monomer) is greater than 0.00001. The moleratio is greater than 0.0005 in another embodiment, greater than 0.001in yet another embodiment, less than 10 in yet another embodiment, lessthan 5 in yet another embodiment, less than 3 in yet another embodiment,and less than 0.10 in yet another embodiment, wherein a desirable rangemay comprise any combination of any upper mole ratio limit with anylower mole ratio limit described herein. Expressed another way, theamount of hydrogen in the reactor at any time may range to up to 10 ppmin one embodiment, or up to 100 or 3000 or 4000 or 5000 ppm in otherembodiments, or between 10 ppm and 5000 ppm in yet another embodiment,or between 100 ppm and 2000 ppm in another embodiment.

A reactor monitored and optionally also controlled in accordance withsome embodiments of the invention can be an element of a staged reactoremploying two or more reactors in series, wherein one reactor mayproduce, for example, a high molecular weight component and anotherreactor may produce a low molecular weight component.

A reactor monitored and optionally also controlled may implement aslurry or gas phase process in the presence of a metallocene ormetallocene-type catalyst system and in the absence of, or essentiallyfree of, any scavengers, such as triethylaluminum, trimethylaluminum,tri-isobutylaluminum and tri-n-hexylaluminum and diethyl aluminumchloride, diethyl zinc and the like. By “essentially free”, it is meantthat these compounds are not deliberately added to the reactor or anyreactor components, and if present, are present to less than 1 ppm inthe reactor.

A reactor monitored may employ one or more catalysts combined with“continuity additives” or other “antistatic agents” to control reactorstatic, as described in U.S. Patent Application Publication No.2005/0148742. In some embodiments, the continuity additive is ametal-fatty acid compound (such as aluminum stearate), which is fed tothe reactor in amounts up to 50 ppm (based on the polymer productionrate. In other embodiments, the continuity additive can be an antistaticagent, such as an ethoxylated or methoxylated amine, an example of whichis Kemamine AS-990 (ICI Specialties, Bloomington Del.) (or combinationsthereof). Other antistatic compositions include the Octastat family ofcompounds, more specifically Octastat 2000, 3000, and 5000. Otherembodiments may include combinations of metal-fatty acids and antistaticcompounds in amounts up to 100 ppm based on the polymer production rate.

In a reactor monitored and optionally also controlled in accordance withsome embodiments of the invention, supported catalyst(s) may be combinedwith up to 6 wt % of continuity additives, prior to introduction to thereactor. The continuity additives are added to the catalyst by tumblingand/or other suitable means. In Catalyst A, for example, 3.0 wt % ofaluminum stearate and 2.0 wt % Kemamine AS-990 are combined with thecatalyst, prior to its introduction to the reactor.

In other embodiments, the metal fatty acids and/or antistatic agents areadded as one or more separate feeds to the reactor; for example, as aslurry of the additive or antistatic agent in hydrocarbon diluents, as asolution in hydrocarbon diluents, or as a direct feed of solid particles(preferably as powders). One advantage of this method of addition isthat it permits on-line adjustment of the feed rate of the additive,independent of the rate of catalyst feed. In other embodiments, thecontinuity additive(s) is added to the recycle line.

Examples of polymers that can be produced include the following:homopolymers and copolymers of C₂-C₁₈ alpha olefins; polyvinylchlorides, ethylene propylene rubbers (EPRs); ethylene-propylene dienerubbers (EPDMs); polyisoprene; polystyrene; polybutadiene; polymers ofbutadiene copolymerized with styrene; polymers of butadienecopolymerized with isoprene; polymers of butadiene with acrylonitrile;polymers of isobutylene copolymerized with isoprene; ethylene butenerubbers and ethylene butene diene rubbers; and polychloroprene;norbornene homopolymers and copolymers with one or more C₂-C₁₈ alphaolefin; terpolymers of one or more C₂-C₁₈ alpha olefins with a diene.

Monomers that can be present in a reactor monitored and optionally alsocontrolled include one or more of: C₂-C₁₈ alpha olefins such asethylene, propylene, and optionally at least one diene, for example,hexadiene, dicyclopentadiene, octadiene including methyloctadiene (e.g.,1-methyl-1,6-octadiene and 7-methyl-1,6-octadiene), norbornadiene, andethylidene norbornene; and readily condensable monomers, for example,isoprene, styrene, butadiene, isobutylene, chloroprene, acrylonitrile,cyclic olefins such as norbornenes.

Fluidized bed polymerization can be monitored and optionally alsocontrolled in accordance with some embodiments of the invention. Thereaction can be any type of fluidized polymerization reaction and can becarried out in a single reactor or multiple reactors such as two or morereactors in series.

In various embodiments, any of many different types of polymerizationcatalysts can be used in a polymerization process monitored andoptionally also controlled. A single catalyst may be used, or a mixtureof catalysts may be employed, if desired. The catalyst can be soluble orinsoluble, supported or unsupported. It may be a prepolymer, spray driedwith or without a filler, a liquid, or a solution, slurry/suspension ordispersion. These catalysts may be used with cocatalysts and promoterswell known in the art. Typically the cocatalysts and promoters mayinclude alkylaluminums, alkylaluminum halides, alkylaluminum hydrides,as well as aluminoxanes. For illustrative purposes only, examples ofsuitable catalysts include Ziegler-Natta catalysts, chromium basedcatalysts, vanadium based catalysts (e.g., vanadium oxychloride andvanadium acetylacetonate), metallocene catalysts and other single-siteor single-site-like catalysts as well as constrained geometry catalysts,cationic forms of metal halides (e.g., aluminum trihalides), anionicinitiators (e.g., butyl lithiums), cobalt catalysts and mixturesthereof, nickel catalysts and mixtures thereof, iron catalysts andmixtures thereof, rare earth metal catalysts (i.e., those containing ametal having an atomic number in the Periodic Table of 57 to 103), suchas compounds of cerium, lanthanum, praseodymium, gadolinium andneodymium.

In various embodiments, a polymerization reaction monitored andoptionally also controlled can employ other additives, such as (forexample) inert particulate particles.

It is to be understood that while the invention has been described inconjunction with the specific embodiments and examples thereof, theforegoing description is intended to illustrate and not limit the scopeof the invention. Other aspects, advantages and modifications will beapparent to those skilled in the art to which the invention pertains.

The phrases, unless otherwise specified, “consists essentially of” and“consisting essentially of” do not exclude the presence of other steps,elements, or materials, whether or not, specifically mentioned in thisspecification, as along as such steps, elements, or materials, do notaffect the basic and novel characteristics of the invention,additionally, they do not exclude impurities normally associated withthe elements and materials used.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, within a range includes everypoint or individual value between its end points even though notexplicitly recited. Thus, every point or individual value may serve asits own lower or upper limit combined with any other point or individualvalue or any other lower or upper limit, to recite a range notexplicitly recited.

All priority documents are herein fully incorporated by reference forall jurisdictions in which such incorporation is permitted and to theextent such disclosure is consistent with the description of the presentinvention. Further, all documents and references cited herein, includingtesting procedures, publications, patents, journal articles, etc. areherein fully incorporated by reference for all jurisdictions in whichsuch incorporation is permitted and to the extent such disclosure isconsistent with the description of the present invention.

What is claimed is:
 1. A method for using at least one static probeduring performance of a polymerization reaction in a fluid bed reactorsystem to monitor a coating on a surface of the reactor system and adistal portion of said at least one static probe, wherein the coating isexposed to flowing fluid within the system during performance of themethod, said method including steps of: (a) during a first interval oftime during performance of the reaction in the reactor system, operatingsaid at least one static probe to generate high speed data indicative ofbubbling in the fluid bed; and (b) determining from the high speed dataat least one electrical property of the coating; wherein the firstinterval of time includes a set of subintervals, and step (b) furtherincludes the steps of: determining cross correlated values, bydetermining for said each subinterval of the first interval, a crosscorrelation of the high speed data generated in the subinterval with oneof said high speed data generated in the subinterval and a processedversion of said high speed data generated in the subinterval; anddetermining electrical potential in the fluid bed during said eachsubinterval of the first interval from the high speed data and the crosscorrelated values.
 2. The method of claim 1, wherein said surface of thereactor system is a bed wall and the coating is exposed to flowing fluidwithin the fluid bed during the reaction.
 3. The method of clam 1,wherein the coating is a film of polymer.
 4. The method of claim 1,wherein the high speed data include frequency components in a range fromabout 1 Hz to about 10 Hz, and the first interval is at least one minutein duration.
 5. The method of claim 4, wherein the high speed data aregenerated by sampling the output of the said at least one static probewith a sampling frequency of at least 100 Hz.
 6. The method of claim 4,wherein the coating is a film of polymer having thickness less than 0.50millimeters.
 7. The method of claim 1, wherein at least one saidelectrical property is a breakdown voltage of the coating.
 8. The methodof claim 1, wherein the first interval of time includes a set ofsubintervals, the high speed data are indicative of average power drawnby the probe due to current induced in the probe by charge in the fluidbed during said each subinterval of the first interval, and step (b)includes the step of: determining electrical potential in the fluid bedduring said each subinterval of the first interval from the high speeddata.
 9. The method of claim 1, wherein the cross correlated values areindicative of movement of bubbles in the fluid bed past the staticprobe.
 10. The method of claim 1, also including the steps of: (c) afterstep (a) but during a second interval of time during performance of thereaction in the reactor system, operating the static probe to generatean additional high speed data indicative of bubbling in the fluid bed;(d) determining from the additional high speed data at least oneelectrical property of the coating; and (e) in response to theelectrical properties determined during steps (b) and (d), monitoring atleast one of deterioration and contamination of the coating over time.11. The method of claim 1, wherein said at least one static probe is abifunctional static probe comprising: an insulated probe having anelectrically insulating distal portion, coated with a portion of saidcoating that is exposed during step (a) to said flowing fluid, and aconductive proximal portion in contact with the distal portion; and anelectrically conducting bare probe, positioned coaxially with theinsulated probe and having an electrically conducting distal surfacecoated with another portion of said coating that is exposed during step(a) to said flowing fluid.
 12. A bifunctional static probe configuredfor use in monitoring a polymerization reaction in a fluid bed reactorsystem according to the method of claim 1, including: an insulated probehaving an electrically insulating distal portion configured to beexposed during said monitoring to flowing fluid within the reactorsystem, and a conductive proximal portion in contact with the distalportion; and an electrically conducting bare probe, positioned coaxiallywith the insulated probe and having an electrically conducting distalsurface configured to be exposed during said monitoring to the flowingfluid within the reactor system.
 13. The static probe of claim 12,wherein the bare probe is at least substantially cylindrical, theinsulated probe is at least substantially annular, and the distalsurface of the bare probe is aligned with a distal surface of theinsulated probe's insulating distal portion.
 14. The bifunctional staticprobe of claim 12, also including electrical insulation between theinsulated probe and the bare probe for insulating said insulated probefrom said bare probe.
 15. The bifunctional static probe of claim 12,wherein the bare probe has an outer side surface, the insulated probehas an inner side surface facing the bare probe's outer side surface,and the bifunctional static probe includes electrical insulation betweenthe insulated probe's inner side surface and the bare probe's sidesurface for insulating the insulated probe from the bare probe.
 16. Thebifunctional static probe of claim 12, wherein said bifunctional probeincludes readout circuitry coupled to the bare probe and to theinsulated probe, wherein the readout circuitry is configured to assertsimultaneously a bare probe output indicative of direct current flowfrom the fluid bed of the reactor system to a surface of the bare probe,and an insulated probe output indicative of inductive current flow fromthe fluid bed to the insulated probe.
 17. A method for using at leastone static probe during performance of a polymerization reaction in afluid bed reactor system to monitor a coating comprising a film ofpolymer on a surface of the reactor system and a distal portion of saidat least one static probe, where the coating is exposed to flowing fluidwithin the reactor system during the reaction, said method includingsteps of: (a) during performance of the reaction in the reactor system,operating the static probe to generate high speed data indicative offluid flow variation in the reactor system during a first interval oftime; and (b) determining from the high speed data at least oneelectrical property of the coating; wherein the first interval of timeincludes a set of subintervals, and step (b) further includes the stepsof: determining cross correlated values, by determining for said eachsubinterval of the first interval, a cross correlation of the high speeddata generated in the subinterval with one of said high speed datagenerated in the subinterval and a processed version of said high speeddata generated in the subinterval; and determining electrical potentialin the fluid bed during said each subinterval of the first interval fromthe high speed data and the cross correlated values.
 18. The method ofclaim 17, wherein said surface of the reactor system is a surface of anentrainment zone of said reactor system.
 19. The method of claim 17,wherein said surface of the system is a bed wall and the flow region isthe fluid bed of the reactor system.